The present invention relates to an apparatus for manufacturing a liquid crystal panel and a method thereof. More particularly, it relates to an apparatus for manufacturing a liquid crystal panel and a method thereof in which two substrates are faced to each other with spacers interposed therebetween, and while applying pressure to these substrates, adhesive arranged at peripheral portions are cured to be adhered to the substrates.
FIGS. 6 and 7 are schematic, sectional views for explaining a manufacturing method by means of a fixing apparatus for a liquid crystal panel as described in Japanese Unexamined Patent Publication No. 88018/1982. In FIGS. 6 and 7, 1 and 2 denote a pair of upper and lower substrates which are a color filter substrate and a TFT substrate having desired patterns formed thereon. Between the upper substrate 1 and the lower substrate 2, there are provided a plurality of spacers 51 of approximately 5 microns for maintaining the clearance, and the upper substrate 1 and the lower substrate 2 are fixedly attached together at their peripheral portions via adhesive 52. This adhesive 52 finally serves as a bulkhead for enclosing liquid crystal within the substrates 1,2. 53 denotes a base (surface plate) that is made, for instance, of stainless steel, and 54 denotes a bendable material which covers at least one of the substrates. The bendable material might be a polyester film or silicone rubber sheet.
According to this conventional manufacturing method for a panel, the spacers 51 are dispersed on an inner surface of either of the upper and lower substrates 1,2 and after applying adhesive to a peripheral portion of the other substrate, both are overlapped at high positioning accuracy. Further, the whole temperature is raised while applying pressure to the substrates, the adhesive 52 is cured, and the upper and lower substrates 1,2 are fixedly attached together without generating any shifts.
At this time, the substrates are maintained in a vessel comprising at least partly of a bendable material, at least one of the substrates is covered with the bendable material, and fixing of the substrates is performed in a condition in which the interior of the vessel is decompressed or pressure is applied on the vessel from the exterior. By the above arrangements, pressure can be applied to the substrates in an uniform manner.
Such a method in which the substrates are applied with pressure by means of a material having bendable characteristics is effective in remarkably improving the uniformity of pressure application than compared to methods in which surface plates of high rigidity are employed. Consequently, irregularities or uniformities in display owing to deficiencies in gaps can be decreased.
A manufacturing method for panels employing a heating method is proposed in Japanese Unexamined Patent Publication No. 232420/1993. As shown in FIG. 8, there are respectively provided a plurality of hot plates 55 above and below substrates 1,2 in this method so that the whole panel can be heated. With this arrangement, characteristics such as rapid heating and soaking can be improved than compared to a method in which a side surface of the panel is heated employing a heater in a furnace.
However, while the manufacturing method according to FIGS. 6 and 7 is effective to some extent with respect to deficiencies in gaps, it cannot prevent shifts in lateral directions of the upper and lower substrates 1,2 or generation of wraps in the substrates. Especially in cases in which two pairs of substrates have been arranged in an aligning manner in a single vessel for the sake of improving productivity, it was found that the shift in lateral directions became larger. Further, this method presents a drawback that the substrates are apt to camber, depending on the way of heat transmission, since heating of the substrates 1,2 is performed in a furnace. That is, when heat is transmitted from downward the furnace, there is generated wrap like a bimetal, since the surface plate 53 of stainless steel is first heated, and since the thermal expansion coefficient of the surface plate 53 of stainless steel is larger than those of the substrates 1,2. If the wrap in the substrate becomes not less than a certain value, it cannot be assembled into a product and thus becomes a defective article. Especially, since requirements with respect to shapes of substrates are becoming increasingly higher accompanying requirements of thin-sizing of products in these years, this results in a drawback that the yield is further decreased. In case a gradually heating process or a method in which the rigidity is increased (the thermal capacity is increased) is employed for the sake of preventing cambers, it will not be acceptable in terms of productivity.
On the other hand, in the method of FIG. 8 in which hot plates 55 are employed, heat is transmitted from the upper and lower substrates so that occurrence of wraps is decreased; however, it cannot prevent shifts of the upper and lower substrates in lateral directions by several xcexcm, and in case request for the positioning accuracy become higher for the sake of improving the performance of liquid crystal, shifts between substrates will not be within acceptable values. Further, it has become relevant from experiments that in the prior art arrangement, the amount of shift became larger, than compared to a case in which the substrates 1,2 are disposed in the center of the surface plate, when they were shifted from the center or when small substrates have been disposed in an aligning manner. From these results, it has become relevant from experiments that shear stress is generated between the surface plate and the substrate and between both substrates owing to differences in coefficients of thermal expansion of upper and lower surface plates or differences in friction coefficients between a surface plate and a substrate depending on the position of the substrates and the upper and lower surface plates. Power is most apt to be released especially between substrate 1 and substrate 2 that are adhered to each other only at their peripheral portions by means of soft adhesive (that is cured after heating) so that shift is generated between the substrates 1,2.
While increase of thermal capacity of the hot plates is effective for securing soaking characteristics in this conventional method, it presented a drawback that this was performed at the expense of heating/cooling speed.
Further, in surface plates made of stainless steel that are designed to be flat at a room temperature, undulations might occur in the surface plates themselves depending on the temperature distribution in the surface plates. Therefore, there was presented a drawback that wraps occurred in substrates that were fixedly attached as to be parallel thereto at a certain area of dispersion.
The present invention has been made in view of the above circumstances, and it is an object thereof to provide a manufacturing apparatus for a liquid crystal panel and a method thereof capable of decreasing amounts of overlapping shifts after fixing two substrates.
In accordance with a first aspect of the present invention, there is provided an apparatus for manufacturing a liquid crystal panel in which two substrates are faced to each other with spacers interposed therebetween, applied with heat and pressure in an overlapped condition, and adhesive arranged between the two substrates is cured for fixing, characterized in that at least one of a pair of pressurizing plates for applying pressure to the two substrates is a graphite plate and in that upper and lower pressurizing plates are made to be of different rigidity.
It is preferable that at least one of the pressurizing plates is of a multi-layered arrangement, and a graphite plate is employed as a part of the multi-layered arrangement.
The pressurizing plate of multi-layered arrangement is preferably provided with an inner space in at least one point positioned between the layers.
It is preferable that the pressurizing plate of multi-layered arrangement is provided with a path for cooling at a nearer side with respect to the substrate and with a heater at a farther side with respect to the substrate.
A coating film is preferably provided on a surface of the graphite plate.
It is preferable that a graphite plate of high rigidity is fixed to a base by means of a pin or a heat insulator in order to deform a surface of the graphite plate in a convex or concave manner.
It is preferable that there is provided a mechanism in which a closed space is formed by means of a pressurizing plate of low rigidity and an upper lid, and a substrate disposed in an exterior space with respect to the closed space is applied with pressure by making a pressure of the closed space higher relative to the exterior space.
It is preferable that a frame body of a thickness approximately identical to that of the two substrates is arranged between the pair of pressurizing plates as to enclose the substrates, wherein the frame body is formed of tungsten, molybdenum, alloys thereof, graphite or iron-nickel alloy.
It is preferable that differences in level are provided in the frame body, wherein the differences in level are set such that a height of an inner surface located on the side of the substrate is identical to or lower than the height of the substrate, and that a height of an outer surface on the opposing side is higher than the height of the inner surface.
In accordance with a second aspect of the present invention, there is further provided a method for manufacturing a liquid crystal panel in which two substrates are faced to each other with spacers interposed therebetween, applied with heat and pressure in an overlapped condition, and adhesive arranged between the two substrates is cured for fixing, characterized in that at least one of a pair of pressurizing plates for applying pressure to the two substrates is a graphite plate and in that upper and lower pressurizing plates are made to be of different rigidity.
According to the present invention, the arrangement for applying pressure to the substrates is composed of a graphite plate of thermal expansion coefficient close to that of a glass substrate and of a plate of low rigidity, and the pressurizing plate of low rigidity is made to stick to the substrate by providing differences in rigidity, shifts in substrates can be prevented while securing uniformity in gaps between substrates.
According to another embodiment of the present invention, at least one of the pressurizing plates is made to be of multi-layered arrangement, and graphite plate is used at a part thereof. Further, a space has been provided at least at one portion between layers of this pressurizing plate of multi-layered arrangement. With these arrangements, soaking characteristics and flatness of the graphite plate can be improved.
According to a further embodiment of the present invention, the pressurizing plate of multi-layered arrangement is provided with a path for cooling on a nearer side with respect to the substrate and a heater on a farther side with respect to the substrate. With this arrangement, rapid cooling/heating is enabled.
According to a yet further embodiment of the present invention, a coating film is provided on the surface of the graphite plate. With this arrangement, long life of the graphite plate is enabled, and improvements in yield are also enabled.
According to a still further embodiment of the present invention, in order to deform the surface of the graphite plate in a convex or concave manner, the graphite plate of high rigidity is fixed by means of a plurality of pins or heat insulator. With this arrangement, it is enabled to control the shape of the finished substrate.
According to another embodiment of the present invention, there is provided a mechanism in which a closed space is formed by means of a pressurizing plate of low rigidity and an upper lid, and a substrate disposed in an exterior space with respect to the closed space is applied with pressure by making a pressure of the closed space higher relative to the exterior space. With this arrangement, occurrence of bubbles is prevented since adhesive that is applied between the substrates will not be exposed to decompression, and consequently, leakage of liquid crystal can be prevented.
According to a further embodiment of the present invention, a frame body of a thickness approximately identical to that of the two substrates is arranged between the pair of pressurizing plates as to enclose the substrates, wherein the frame body is formed of tungsten, molybdenum, alloys thereof, graphite or iron-nickel alloy. With this arrangement, the pressurizing plates are made to uniformly contact with the substrates in flat conditions.
According to a still further embodiment of the present invention, differences in level are provided in the frame body, wherein the differences in level are set such that a height of an inner surface located on the side of the substrate is identical to or lower than the height of the substrate, and that a height of an outer surface on the opposing side is higher than the height of the inner surface, so that the pressure in the peripheral portions of the substrates can be heightened and the adhesive can be smashed in a stable manner. With this arrangement, shifts of substrates can be further decreased and uniformity in gaps between substrates can be secured.
According to the method of the present invention, two substrates are applied with pressure by employing a graphite plate for at least one of a pair of pressurizing plates for applying pressure to the two substrates and upper and lower pressurizing plates are made to be of different rigidity. With this arrangement, the graphite plate of low rigidity is made to stick to the substrate so that shifts between substrates can be prevented while securing uniformity in gaps between substrates.